The invention relates to a device for modifying the control times of gas-exchange valves of an internal combustion engine according to the preambles of Claims 1 and 6.
In internal combustion engines, camshafts are used for actuating the gas-exchange valves. Camshafts are mounted in the internal combustion engine such that cams mounted on these camshafts contact cam followers, for example, cup tappets, rocker arms, or finger levers. If the camshaft is set in rotation, then the cams roll on the cam followers, which in turn actuate the gas-exchange valves. Thus, both the opening period and also the amplitude, as well as the opening and closing times of the gas-exchange valves, are set by the position and the shape of the cams.
Modern engine concepts allow variable valve train designs. On one hand, the valve lift and valve opening period should be made variable up to complete shutdown of individual cylinders. For this purpose, concepts such as switchable cam followers, variable valve trains, or electrohydraulic or electrical valve actuators are provided. Furthermore, it has been shown to be advantageous to be able to influence the opening and closing times of the gas-exchange valves during the operation of the internal combustion engine. It is likewise desirable to be able to influence the opening or closing times of the inlet or outlet valves separately, in order, for example, to be able to selectively set a defined valve overlap. By setting the opening or closing times of the gas-exchange valves depending on the current engine-map range, for example, the current rotational speed or the current load, the specific fuel consumption can be lowered, which has a positive effect on the exhaust-gas behavior and increases the engine efficiency, the maximum torque, and the maximum output.
The described variability in the gas-exchange valve time control is implemented through a relative change of the phase position of the camshaft relative to the crankshaft. Here, the camshaft is usually in a driven connection with the crankshaft via a chain drive, belt drive, gearwheel drive, or equivalent drive concepts. Between the chain drive, belt drive, or gearwheel drive driven by the crankshaft and the camshaft there is a camshaft adjuster, which transmits the torque from the crankshaft to the camshaft. Here, this device for modifying the control times of the internal combustion engine is constructed such that during the operation of the internal combustion engine, the phase position between the crankshaft and camshaft is held reliably and, if desired, the camshaft can be rotated within a certain angular range relative to the crankshaft.
In internal combustion engines with separate camshafts for the intake and exhaust valves, these can each be equipped with a camshaft adjuster. Therefore, the opening and closing times of the intake and exhaust gas-exchange valves can be shifted in time relative to each other and the valve overlaps are set selectively.
The seat of modern camshaft adjusters is generally located on the drive-side end of the camshaft. It is comprised of a crankshaft-fixed drive wheel, a camshaft-fixed driven element, and an adjustment mechanism transmitting the torque from the drive wheel to the driven part. The drive wheel can be constructed as a chain, belt, or gearwheel and is locked in rotation with the crankshaft by means of a chain, belt, or gearwheel drive. The adjustment mechanism can be operated electromagnetically, hydraulically, or pneumatically. Mounting the camshaft adjuster on an intermediate shaft or supporting it on a non-rotating component is similarly conceivable. In this case, the torque is transmitted via additional drives to the camshaft.
Electrically operated camshaft adjusters are comprised of a drive wheel, which is in driven connection with the crankshaft of the internal combustion engine, a driven part, which is in driving connection with a camshaft of the internal combustion engine, and adjustment gearing. The adjustment gearing involves a triple-shaft gear mechanism, with three components rotating relative to each other. Here, the first component of the gearing is locked in rotation with the drive wheel and the second component is locked in rotation with the driven part. The third component is constructed, for example, as a toothed component, whose rotational speed can be regulated via a shaft, for example, by means of an electric motor or a braking device.
The torque is transmitted from the crankshaft to the first component and from there to the second component and thus to the camshaft. This happens either directly or under intermediate connection of the third component.
Through suitable regulation of the rotational speed of the third component, the first component can be rotated opposite the second component and thus the phase position between the camshaft and crankshaft can be changed. Examples for such triple-shaft gear mechanisms are internal eccentric gear mechanisms, double-internal eccentric gear mechanisms, shaft gear mechanisms, swashplate gear mechanisms, or the like.
For controlling the camshaft adjuster, sensors detect the characteristic data of the internal combustion engine, for example, the load state, the rotational speed, and the angular positions of the camshaft and crankshaft. This data is fed to an electronic control unit, which controls the adjustment motor of the camshaft adjuster after comparing the data with an engine-map range of the internal combustion engine.
From DE 102 22 475 a device for modifying the control times of an internal combustion engine is known, in which the torque transfer from the crankshaft to the camshaft and the adjustment process are realized by means of a swashplate gear mechanism. The device essentially comprises a camshaft-fixed driven element and a swashplate. The device further has a drive wheel, which is in driven connection with a crankshaft and is constructed in one piece with a housing. The swashplate is provided with four pins engaging in elongated holes of the housing. The torque of the crankshaft is transmitted via the drive wheel, the housing, and the pins to the swashplate.
The device further has an adjustment shaft, which is driven, for example, by an electric motor and on which the swashplate is supported at a defined contact angle.
The swashplate is provided on its axial side surface facing the driven element with conical gearwheel teeth and arranged at a certain contact angle to the driven element, such that an angle segment of the teeth of the swashplate engages in an angle segment of conical gearwheel teeth constructed on the driven element. Here, there is a difference in the number of teeth in the conical gearwheels.
A rotation of the adjustment shaft relative to the driven element leads to a wobbling rotation of the swashplate and thus to a rotation of the engaged angle segment relative to the driven element. Due to the difference in the number of teeth of the conical gearwheels, this leads to relative rotation of the camshaft relative to the crankshaft.
The drive wheel or the housing is supported on an axial shoulder of the driven element so that it can rotate relative to this element. The conical gearwheel teeth of the driven element are constructed on a teeth carrier, wherein the teeth carrier is mounted before the shoulder in the axial direction. The teeth carrier and a cover screwed to the drive wheel form an axial bearing for the drive wheel or the housing. Here, the cover is fixed in the axial direction by the driven element on one side and by the camshaft on the other side.
The construction of a bearing shoulder on the driven element and the teeth carrier arranged offset axially to this element lead to a relatively large need for axial installation space for the device and to a complex geometrical shape for the driven element.
Furthermore, the driven element is locked in rotation with the camshaft by means of an attachment screw. The screw head engages from the side facing away from the camshaft through the device, wherein its threads engages in complementary internal threads constructed in the camshaft. The screw head exerts a force on the driven element, whereby this is fixed to the camshaft.
The screw head is used simultaneously as the race for the cylinder bodies of a needle bearing, by means of which the adjustment shaft is supported on the screw head. In order to be able to be used as the race for the needle bearing, the screw head must be subjected to a hardening process, wherein care must be taken that the threaded section is not hardened. Such hardening processes are complicated and expensive. Simultaneously, the solid screw head leads to a high mass and thus to a high inertia of the arrangement.